Touch interface devices can include computing devices having touch sensitive surfaces used to receive input from operators of the devices. For example, many smart phones, tablet computers, and other devices have touch sensitive screens that identify touches from operators as input to the devices. Haptic or tactile feedback from such screens has emerged as a highly sought feature.
Effective mechanisms for producing such a physical sensation have been lacking. Some known mechanisms include vibrating the entire device, while in others the screen is tapped or “popped”, or the screen is shimmied laterally. Interesting haptic effects can be produced, but the effects fall short of the kind of tactile sensations that one encounters in touching an actual textured surface, or a device that has physical buttons or ridges or other physical haptic features.
Buttons in particular are a high priority. In touching a real button, a user's fingers are sensitive to the edges of the button, so that the location of the button is evident and the user has confidence, without looking, of being properly registered or aligned to the button.
Touch is an “active sense,” as it is fundamentally an interplay of the user's motion with the sensations received. Touch is seldom employed without motion. The sensation of touching a button or another feature—such as a ridge, bump, curve, etc—may benefit from several modes of touch, which are generally used in combination.
A first mode is due to the pattern of force indenting the surface of the fingertip. This can be thought of as a static phenomenon, as, in principle, one could perceive a pattern just by pressing a fingertip into contact with a surface. In practice the perception of a pattern is enhanced by sliding the fingertip across it, much as a reader of Braille slides a finger across a Braille character, rather than pressing a finger onto it.
An additional mode is the guiding of fingertip motion that an edge or pattern presents. This mode seems to require (not just be enhanced by) motion of the fingertip. A sensation of letting the surface guide the finger's motion is experienced. An example is following a ridge line, display edge, or the edge of a button that is large compared to the fingertip. Arrays of controls (buttons and switches) in vehicles present many such haptic features, to reduce reliance on vision. Other devices with which one wishes to become haptically familiar also tend to have strong haptic features, e.g. musical instruments.
Additionally, lateral forces may be perceived even when there is no ongoing finger motion at a given moment. For instance, a user may have pushed a finger up against a button edge or haptic feature, and left it in contact there, so that a lateral force continues to push back.